For upgrading to 2 colours, you need extra extruder and heater drives, which means you need either the DueX4 or the Duet shield, assuming you don't want to make your own electronics.
To use the DueX4, you need to print a new enclosure to accommodate it and the Duet. There is an issue with noise on the additional hot end thermistor readings, although there are a couple of workarounds for it. I cover how I upgraded to dual nozzle using a DueX4 in my blog, see [
miscsolutions.wordpress.com]. This dates from last year, well before RepRapPro produced their dual nozzle upgrade, so it lacks nice features such as the quick set nozzle.
The Duet shield is easier to use than the X4 because it just plugs on top of the Duet. One slight complication is that the bottom edge of the board overlaps the Duet slightly, which meant that it wouldn't fit in my enclosure. I ended up cutting 2mm off the bottom edge of the board with a hacksaw, rather than modify and reprint the enclosure. The shield doesn't have the thermistor noise issue of the DueX4.
So I recommend using the shield rather than the X4, unless you think you will need more than 2 additional heater and stepper motor drives in the future. I am hopeful that the shield may also cost less than the DueX4 because it contains fewer components; although RRP didn't list it on their web shop last time I looked, so this remains to be seen.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
O you have better solution of Colour Upgrade for Ormerod 1?